This application relates to proteins which are involved in the growth, regulation or maintenance of nervous tissue. In particular, it relates to a nerve-derived factors having homology to NGF.
Nerve growth factor (NGF) is a protein which has prominent effects on developing sensory and sympathetic neurons of the peripheral nervous system. NGF acts via specific cell surface receptors on responsive neurons to support neuronal survival, promote neurite outgrowth, and enhance neurochemical differentiation. NGF actions are accompanied by alterations in neuronal membranes (Connolly et al., 1981, J. Cell. Biol: 90:176; Skaper and Varon, 1980, Brain Res. 197:379), in the state of phosphorylation of neuronal proteins (Yu, et al., 1980, J. Biol. Chem. 255:10481; Haleqoua and Patrick, 1980, Cell 22:571), and in the abundance of certain mRNAs and proteins likely to play a role in neuronal differentiation and function (Tiercy and Shooter, 1986, J. Cell. Biol. 103:2367).
Forebrain cholinergic neurons also respond to NGF and may require NGF for trophic support. (Hefti, 1986, J. Neurosci., 6:2155). Indeed, the distribution and ontogenesis of NGF and its receptor in the central nervous system (CNS) suggest that NGF acts as a target-derived neurotrophic factor for basal forebrain cholinergic neurons (Korsching, November/December 1986, Trends in Neuro. Sci., pp 570-573).
While a number of animal homologues to NGF have become known, it was not until recently that an apparently distinct nerve growth factor was identified that nonetheless bears some homology to NGF (Leibrock et al., 1989, Nature 341:149). This factor, called brain-derived neurotropic factor (BDNF), now also called NT-2, was purified from pig brain, and a partial amino acid sequence determined both from the N-terminal end and from fragments purified after cleavages. The longest sequence, compiled from several overlapping fragments, was used to synthesize two sets of oligonucleotides that were used to prime the amplification of a pig genomic template using the polymerase chain reaction (PCR). The nucleotide sequence between the two primers was determined and used to synthesize specific primers for further PCRs on a complementary DNA template obtained by reverse transcription of total RNA isolated from the superior colliculus of the pig brain. The nucleotide sequence so obtained contained an opening reading frame coding for a protein of 252 amino acids, starting with the first methionine codon found after four in-frame stop codons. Leibrock, et al. speculate that there is no reason to think that BDNF and NGF should be the only members of a family of neurotropic proteins having in common structural and functional characteristics, and the authors hope that these common structural features could be used to aid the discovery of other members.
More recently, another novel neurotrophic factor closely related to xcex2NGF and BDNF was discovered, called neuronal factor (NF), or neurotrophin-3 (NT-3). (Hohn, et al., 1990, Nature 344:339; Maisonpierre, et al., 1990, Science 247:1446; Rosenthal, et al., 1990, Neuron 4:767. Both BDNF and NT-3 share approximately 50% of their amino acids with xcex2NGF. High levels of mRNA coding for BDNF and NT-3 occur in the adult rodent brain. xcex2NGF, BDNF, and NT-3 support survival of selected populations of chick sensory neurons, suggesting independent roles in the regulation of neuronal survival during development.
Neuronal survival and growth is also affected by growth factors for non-neuronal cells, including fibroblast growth factor (FGF), epidermal growth factor, and insulin-like growth factors. (Morrison, et al., 1987, Science 238:72; Walicke, 1988, J. Neurosci. 8:2618; Bhat, 1983, Dev. Brain Res. 11:315). Basic FGF (bFGF) supports initial survival and subsequent fiber outgrowth of dissociated rodent fetal neurons in culture. While neurons from many brain regions are affected, the proportion of neurons surviving varies among brain regions, suggesting that subpopulations of neurons are responsive to bFGF. (Morrison, et al., 1986, Proc. Natl. Acad. Sci. 83:7537; Walicke, et al., 1986, Proc. Natl. Acad. Sci. USA 83:3012). Since bFGF lacks a signal sequence typical for released proteins, and since bFGF levels present in the brain are much larger than those of xcex2NGF and BDNF, it has been questioned whether bFGF plays a physiological role as neurotrophic factor and has been proposed that bFGF acts as xe2x80x9cinjury factorxe2x80x9d released in events involving cellular destruction. (Thoenen, et al., 1987, Rev. Physiol. Biochem. Pharmacol. 109:145).
Another neurotrophic factor having potential therapeutic use for peripheral nervous system disorders, ciliary neurotrophic factor (CNTF), has been cloned and expressed. (Lin, et al., 1989, Science, 246:1023). CNTF, which was purified from adult rabbit sciatic nerves, acts on the peripheral nervous system and appears to be completely unrelated to NGF.
It is an object to identify a fourth neurotrophic factor in the NGF family and to obtain nucleic acid encoding such a factor.
It is another object to synthesize such a new factor in recombinant cell culture.
It is yet another object to provide variants and modified forms of such a new factor.
It is an additional object to prepare immunogens for raising antibodies, as well as to obtain antibodies, capable of binding such a new factor or variant or modified form thereof.
Another object is to provide diagnostic and therapeutic compositions comprising such a new factor or variant or modified forms thereof, and methods of therapeutic treatment.
These and other objects of the invention apparent to the ordinary artisan are accomplished by first providing a nucleic acid sequence comprising at least a portion of the coding sequence for a new nerve-derived factor related to NGF, BDNF, and NT-3, hereafter termed neurotrophic factor-4 (NT-4).
In one aspect, the invention provides an isolated nucleic acid encoding NT-4. In another aspect, the invention provides a vector comprising this nucleic acid. In a third aspect, the invention supplies a recombinant host cell comprising this nucleic acid. In yet another aspect, the invention furnishes a composition comprising NT-4 from an animal species, which composition is free of contaminating polypeptides of that animal species.
The nucleic acid encoding NT-4 is also used in hybridization assays to identify and to isolate nucleic acids having substantial sequence homology to the nucleic acid encoding NT-4.
NT-4 or fragments thereof (which also may be synthesized by in vitro methods) are fused (by recombinant expression or in vitro covalent methods) to an immunogenic polypeptide and this, in turn, is used to immunize an animal in order to raise antibodies against an NT-4 epitope. Anti-NT-4 is recovered from the serum of immunized animals. Alternatively, monoclonal antibodies are prepared from cells of the immunized animal in conventional fashion. Antibodies identified by routine screening will bind to NT-4 but will not substantially cross-react with NGF, BDNF, or NT-3. Immobilized anti-NT-4 antibodies are useful particularly in the diagnosis (in vitro or in vivo) or purification of NT-4.
Substitutional, deletional, or insertional mutants of NT-4 are prepared in vitro or recombinant methods and screened for immuno-crossreactivity with NT-4 and for NT-4 antagonist or agonist activity.
NT-4 also is derivatized in vitro in order to prepare immobilized NT-4 and labelled NT-4, particularly for purposes of diagnosis of NT-4 or its antibodies, or for affinity purification of NT-4 antibodies.
NT-4, or a variant or modified form thereof, or anti-NT-4 antibody is formulated into physiologically acceptable vehicles, especially for therapeutic use. Such vehicles include sustained-release formulations.
In another aspect, the invention provides a method for producing NT-4, or a variant or modified form thereof, comprising culturing a transformed host cell and recovering the desired polypeptide from the host cell culture.
NT-4 has been found to have a broad tissue distribution and is structurally related to NGF, BDNF, and NT-3. Its presence in the brain and muscle tissue indicates that it may be useful as a therapeutic agent for neurodegenerative diseases and damaged nerve cells, e.g., nerves damaged as a result of trauma.
Therefore, in another aspect, the invention provides a method for treating a neurodegenerative disease or damaged nerve cells comprising administering to a mammal an effective amount of NT-4, or a variant or modified form thereof.